Mosses could help rapidly detect pollution

Researchers have developed a method that uses mosses to rapidly and cheaply detect sulfur dioxide, a common pollutant from burning fossil fuels.

The method uses a camera to monitor the change of moss leaves from green toward yellow that is triggered by sulfur dioxide within 10 seconds.

Scientists envision using mosses to monitor harmful gases in both indoor and outdoor environments.

Mosses have advantages over traditional sensors, such as not needing to be replaced after detecting the gas.

Drug-sniffing dogs are an accepted part of our modern world. In the near future, could pollution-sniffing mosses be equally common?

Although plants seem inactive compared to animals, a team led by Dr. Xingcai Qin, a chemist at Nanjing University, China, has shown that a common species of moss rapidly responds to sulfur dioxide, a pollutant produced by burning fossil fuels. Monitoring these responses with cameras could rapidly and cheaply detect pollution, the researchers reported recently in Analytical Chemistry.

Cars produce sulfur dioxide, but the biggest sources are power plants and industrial facilities. Sulfur dioxide can harm human health and contributes to smog and acid rain.

Other research groups have shown that mosses can work as pollution indicators, but this new method should be more rapid and easy to apply.

“We hope traffic cameras and security cameras in factories, homes, offices and shopping malls accompanied with plants can be used to monitor gas pollution,” said Qin.

Moss collected from the Nanjing University campus. Courtesy of Xingcai Qin

The idea of using plants as low-cost, environmentally friendly gas sensors was inspired when Qin used plants in his home to help combat gas pollution associated with paint and new furniture in his recently constructed apartment.

Moss leaves are sensitive to pollution since they consist of a single layer of cells that easily absorb material from the environment.

“[Mosses’] relationships with the water and the environment [are] like a piece of tissue paper,” says Brent Mishler, a botanist at the University of California, Berkeley. “If you put a piece of tissue paper on a rock and it rained, it would get wet and then as soon as the sun came out it would dry. That’s pretty much their biology.”

To test using mosses as pollution monitors, Qin’s team collected wild Atrichum undulatum from the Nanjing University campus. The scientists placed the mosses with soil in a detection chamber. They prepared mixtures of different gas concentrations with various humidities in sample bags, then pumped each mixture through the chamber so that the gases flowed over the moss.

A webcam monitored the moss through the transparent top of the chamber. The researchers discovered that about 10 seconds after they introduced sulfur dioxide, the mosses began to change from green to yellow. A computer algorithm analyzed how quickly this change occurred to identify the sulfur dioxide concentration.

Moss in the detection chamber without the webcam attached. Courtesy of Xingcai QinGreen and Yellow moss from before and after exposure to sulfur dioxide. Courtesy of Xingcai Qin

The mosses detected sulfur dioxide at levels of just a few parts per million, the team reported. The method worked for larger ranges of humidities and sulfur dioxide concentrations than many commercial sensors. And unlike sensors that use the color change of a chemical, a moss recovers its sensing capacity if the exposure is nonlethal.

The results make sense to Mishler, who was not involved in the study. “The mosses are really sensitive to these pollutants,” he said.

The team plans to continue testing to address issues for practical applications, such as differences from plant to plant and the effect of the environment. This will involve both indoor and outdoor field tests.

“I think it should be tested in the field,” said Mishler. “People have done field studies using mosses to monitor pollution, but not with remote sensing or a camera.” He also recommends that the team work with a botanist to verify the moss species and preserve a specimen to ensure that other groups can run their own tests.

The team hopes that cameras already in use, such as traffic and security cameras, can turn mosses across cities into real-time, cheap pollutant sensors. The technique may eventually be applicable for large-area pollution monitoring using satellites or drones.

Bailey Bedford (@BBedfordScience) is a graduate student in the Science Communication Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.

Header photo: Beijing smog as seen from the China World Hotel, March 2003, during the SARS outbreak. Photo by Kevin Dooley (@pagedooley on Flickr).